The present invention relates generally to transmitting analog signals. More particularly, the present invention relates to an apparatus for broadband multiplexing of FM signals.
Recently, the rules regarding ownership of FM Broadcast Stations have been relaxed. Consequently, the FM broadcast industry has changed. In particular, FM broadcast stations have been driven to share transmission facilities. By sharing a single antenna and transmission line, the station owners can individually reduce their costs. However, the amount saved by a station owner will be dependent upon the cost of the overall transmission facility.
Typically, Master FM antenna systems are used to consolidate radio frequency (RF) transmission facilities. A Master antenna system may be either a large master antenna system or a small master system. A large master antenna system is more costly than a small master antenna system, and generally utilizes a panel antenna, nine-inch rigid coaxial line, and constant impedance combiner modules. The above configuration for a large master antenna system typically gives the large master antenna system the capability to support ten (10) stations across the entire FM band. In addition to being able to accommodate a wide bandwidth, a typical large master antenna system is also able to deliver high power, and maintain a constant antenna pattern (i.e., radiation pattern). The primary disadvantage of the large master antenna system is its high cost.
A small master antenna system, which is less than a large master antenna system, typically is a side-mounted antenna. Generally, small master antenna systems are capable of accommodating up to three stations. Further, small master antenna systems usually can only accommodate about 5 MHz of bandwidth. Further, the antenna pattern of the FM signal being transmitted may not be constant at all frequencies. Although the small master antenna system is less expensive than the large master antenna system, it does not have the capabilities of the large master antenna system, or perform as well as the large master antenna system. Thus, there is a significant difference, in performance abilities and cost, between the large and small master antenna systems.
An approach to the disparity between the large and small antenna systems was the development of a master antenna system that accommodates up to four FM stations, particularly, Class C stations, over a bandwidth of 13 MHz. Class C stations are authorized to broadcast with a maximum Effective Radiated Power (ERP) of 100 KW, which is the highest power license for FM in the U.S. A design for this master antenna system may include up to sixteen (16) sections of circularized polarized elements in stacked arrays. Typically, a branch feed system is employed for accommodating 12 MHz of bandwidth for a master antenna of this type. The branch feed system will deliver a signal to a feedpoint mouth of the antenna, which is typically 1.5 inches in diameter. The circularly polarized elements, usually consisting of curved dipole members, are arranged in a shape of a helical spiral. Thus, the distance between the curved dipole members remains constant throughout the spiraling shape. Typically, the overall diameter of the helix is 36 inches.
Although, this master antenna system was developed as an alternative to the large and small antenna systems, which have been traditionally used to multiplex FM stations, it suffers in performance when attempts are made to multiplex more than four stations. Further, it suffers when more than 12 MHz of bandwidth is needed.
Accordingly, it is desirable to provide an antenna system designed for broadband multiplexing of FM stations that is capable of accommodating more than four stations across 12 MHz of bandwidth or more, and maintaining excellent performance. Further, it is desirable to provide an antenna system that is able to sustain the power of more than four stations.
The foregoing desired result has been achieved to a great extent by the present invention, which, in one aspect, an antenna system is provided having a first and a second curved dipole member. The first and second dipole member are affixed to opposite ends of a first connecting member wherein said first dipole members form straight lines between their terminal ends when viewed along the axis of the first connecting member. A third and fourth curved dipole member are also provided. The second and third dipole member are affixed to opposite ends of as second connecting member wherein the third and fourth dipole members form straight lines between their terminal ends when viewed along the axis of the second connecting member. The second connecting member intersects said first connecting member, and there is a 36xc2x0 angle between the straight line formed by said first and second curved dipole members and the second connecting member and a 27.5xc2x0 angle between the straight line formed by the third and fourth curved dipole members and the axis of the first connecting member.
In another aspect of the invention, a method of broadcasting a radio frequency signal is provided having the steps of transmitting a radio frequency signal to a quadrapole ring antenna and radiating the radio frequency signal from the antenna. In this method, the quadrapole ring antenna has a first and second dipole member affixed at opposite ends of a first connecting member and wherein the first and second dipole members form straight lines between their terminal ends when viewed along the axis of the first connecting member and wherein there is less than a 36xc2x0 angle between the straight line formed by the first and second dipole member and a plane normal to the first connecting member.
In the foregoing method, the quadrapole ring antenna can also have a third and a fourth dipole member affixed at opposite ends of a second connecting member and wherein the third and fourth dipole members form straight lines between their terminal ends when viewed along the axis of the second connecting member and wherein there is a 327.5xc2x0 angle between the straight line formed by said third and fourth dipole member and a plane normal to the second connecting member.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.